1. Field of the Invention
The present invention relates to electronic devices including a base substrate to be surface-mounted on a circuit board, and a structure of a base substrate board serving as an intermediate product of the electronic device.
2. Description of Related Art
A portable telephone has, for example, an antenna duplexer mounted thereon for sharing one antenna with transmitting system and receiving system. The antenna duplexer is generally provided by a composite device of laminate type as shown in FIG. 9. With the composite device of laminate type, a plurality of ceramic layers 61 are laminated to constitute a base substrate 6 of laminate type, as shown in FIG. 10. An uppermost ceramic layer 61 has a plurality of chip components 7 mounted on a surface thereof. Intermediate ceramic layers 61 are each provided on a surface thereof with circuit elements including inductor patterns and capacitor patterns. The circuit elements and the chip components 7 are connected to each other to provide an antenna duplexer circuit.
Furthermore, with the composite device of laminate type, the base substrate 6 is provided on a side surface 60 with a plurality of external electrodes 20 in the form of a post perpendicular to the base substrate 6 in order to surface-mount the base substrate 6 on a circuit board, as shown in FIG. 9, to expose the external electrodes 20 on a rear surface of the base substrate 6.
When the composite device of laminate type is surface-mounted on the circuit board, the base substrate 6 has a side surface 60 formed with solder filets 30 for covering the external electrodes 20, as shown in FIG. 7(a). The solder fillets 30 mechanically join the base substrate 6 to the circuit board (not shown), and electrically connects the electrodes 20 to the circuit board (JP-B No. 2976049).
It has been required with ever increasing severity that electronic devices such as the composite device of laminate type be reduced in size. This gives rise to the important problem of downsizing a surface mounting area on the circuit board. However, the following problem arises. When the composite device of laminate type is surface-mounted on the circuit board as shown in FIG. 7(a), the solder filets 30 greatly project outward from the side surface 60 of the base substrate 6, resulting in enlarging a surface mounting area A by the amount of projection of the solder fillets 30.